The present invention relates to devices for automatic correction of the orientation of motor-vehicle headlamps, upon variations in the attitude of the vehicles.
It is known that the regulations stipulate that the headlamps of a vehicle be set up so as to illuminate the road effectively in front of the vehicle without, however, dazzling the other drivers. For example, the upper cut-off of a European dipped beam should be inclined to the horizontal with an angle of depression lying between 1 and 1.5 hundredths of a radian.
However, when the vehicle is loaded, or when it accelerates or decelerates, the attitude of the vehicle can vary in large proportions, and the orientation of the headlamps is then no longer in accordance with the legislation: the cut-off is either raised and the headlamps dazzle the other drivers, or depressed and the illumination is completely insufficient.
One solution was first of all to arrange sensors in the vicinity of each wheel of the vehicle so as to determine its attitude, the information originating from these sensors being processed by a computer so as to drive a device for setting-up the orientation of the headlamps appropriately. Such a solution involves arranging wheel sensors at places on the vehicle where the space available is rationed, and additional wiring in the vehicle, the wheel sensors being, moreover, subjected to all the attacks from the outside environment, such that they have to possess excellent protection.
Devices for automatic correction without wiring are also known, for example from the document U.S. Pat. No. 5,193,894. The device described in this document comprises photosensitive cells which detect the variations in brightness of areas of the ground in front of the vehicle, which are illuminated by the headlamp. Processing means derive a signal, on the basis of the measurements from these cells, for the control of an actuator suitable for varying the inclination of the headlamp.
The major drawback of these devices lies in the fact that they are severely disturbed by external illumination such as the street lighting or the headlamps of other vehicles. The measurements taken by the photocells also depend strongly on the more or less reflecting nature of the surfaces illuminated in front of the vehicle. The setting obtained under these conditions is therefore not constant, and suffers substantial deviations depending on the environment of the vehicle.
It has been proposed, for example in the document FR-A-2 759 043, remedy these drawbacks by proposing an installation for setting up the illumination range of the headlamps of a vehicle, comprising a transmission installation which transmits at least one beam of electromagnetic rays falling on a region to the front of the vehicle, an electro-optical detection installation which gives an image point, at least of the irradiated region, an interpretation installation which interprets the position of at least one irradiated region, and produces a signal from it which is compared with a datum signal representing the correct setting of the illumination range, and, in the event of a deviation between the actual signal and the datum signal, setting-up installations are driven so as to cancel out this deviation.
Such an installation, even if it solves the problem of the stray illumination and of the surface states of the road surfacing, nevertheless exhibits drawbacks. This is because the measurements taken by this installation amounts to analysing the movement of a spot of light on the ground in front of the vehicle. It will therefore be understood that, for a constant attitude of the vehicle, the measurements will be disturbed by the variation in the height of the vehicle, that is to say during movements of simultaneous compression or of expansion of all the elements of the suspension of the vehicle, which impart pure vertical-translation movements on the chassis of the vehicle. During such vertical-translation movements, the light spot in front of the vehicle moves, and this is all the more so the further the illuminated area is from the vehicle. The movement of the light spot is then interpreted by the interpretation installation as a change in attitude, the latter then generating an erroneous correction signal for the setting-up installations.
The present invention falls within this context, and its object is to propose a device for automatic correction of the orientation of the headlamps of a motor vehicle in elevation upon variations in the attitude of the vehicle, which do not require the installation of wheel sensors nor their wiring, which is insensitive to variations in the height of the vehicle, which is simple to implement and reliable, while being inexpensive.
Thus the subject of the present invention is a device for automatic correction of the orientation of at least one motor-vehicle headlamp upon variations in the attitude of the motor vehicle, including
an emitter projecting, onto the ground in front of the vehicle, two light spots which are spaced apart in a direction parallel to the longitudinal axis of the vehicle,
a sensor of the illumination of the light spots comprising an objective forming an image of the light spots on a receiver and supplying an output signal for each one,
processing means suitable for deriving a control signal from the output signal from the sensor, and
an actuator controlled by the control signal and able to alter the elevation orientation of a reflector of the headlamp.
According to the present invention, the control signal for the actuator is derived by the processing means on the basis of a linear function of the output signals supplied by the sensor for each image of each light spot.
According to other advantageous and non-limiting characteristics of the invention:
the linear function between the output signals from the sensor for each image of each light spot is of the form dc1xe2x88x92axc3x97dc2=Kxc3x97(xcex8xe2x88x92xcex80)+b, where a, b and xcex80 are constants characteristic of the geometry of the correction device, xcex8 is an angle representative of the attitude of the vehicle, and where K is a magnitude representative of the height of the vehicle;
the emitter and the sensor are fixed with respect to one another;
the emitter and the sensor are integral with a movable part of the vehicle;
the movable part of the vehicle consists of the reflector of a headlamp of the vehicle;
the emitter and the sensor are fixed with respect to the vehicle;
the emitter and the sensor are situated one on a fixed part of the vehicle, the other on a movable part of the vehicle;
the light spots define a straight-line segment substantially parallel to the longitudinal axis of the vehicle;
the emitter and the sensor are situated substantially in the same vertical plane;
the direction of illumination of the emitter and the optical axis of the sensor are contained in the same vertical plane parallel to the longitudinal axis of the vehicle.